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  • Author or Editor: Bingru Huang x
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Drought is a major factor limiting the growth of turfgrasses in many areas. The functional relationship of drought stress and accumulation of various ions in turfgrasses is not well understood. The objective of this study was to investigate the effects of drought on root growth and accumulation of several major nutrients in three tall fescue (Festuca arundinacea Schreb.) cultivars varying in drought tolerance (Falcon II = Houndog V > Rebel Jr). Grasses were grown in well-watered or drying (nonirrigated) soil for 35 days in a greenhouse. Drought conditions limited total root length to a greater extent for `Rebel Jr' than for `Falcon II' and `Houndog V', while specific root length (SRL) was greater in `Falcon II' and `Houndog V' than in `Rebel Jr'. Concentrations of N, P, and Mg decreased, whereas those of K, Ca, and Fe increased, in shoots of drought-stressed plants of all three cultivars. Root N was not affected, but root P decreased in `Rebel Jr', and root K decreased in all three cultivars under drought conditions. Drought reduced the proportions of N and P in shoots and increased those in roots, while increasing the proportion of K in shoots and decreasing that in roots. During drought stress, both `Falcon II' and `Houndog V' maintained higher K concentration in shoots, and `Falcon II' in roots, than did `Rebel Jr', but `Rebel Jr' and `Houndog V' had higher Fe concentration in shoots than did `Falcon II'. The higher K and lower Fe accumulations in shoots could contribute to better drought tolerance of tall fescue cultivars.

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Heat stress symptoms in cool-season plants are characterized by loss of chlorophyll (Chl) and membrane stability, as well as oxidative damage. The objectives of this study were to determine whether foliar application of β-sitosterol, a naturally occurring plant metabolite, may promote heat tolerance by suppressing heat-induced leaf senescence as indicated by the maintenance of healthy turf quality (TQ), and Chl and membrane stability; and to determine its roles in regulating antioxidant metabolism in creeping bentgrass (Agrostis stolonifera). ‘Penncross’ plants were exposed to heat stress (35/30 °C day/night) optimal temperature conditions (nonstressed control, 22/17 °C day/night) for a duration of 28 days in environment-controlled growth chambers. Plants were foliar-treated with β-sitosterol (400 µM) or water only (untreated control) before heat stress, and at 7-day intervals through 28 days of heat stress. Plants treated with β-sitosterol had significantly greater TQ and Chl content, and significantly less electrolyte leakage (EL) than untreated controls at 21 and 28 days of heat stress. Application of β-sitosterol reduced malondialdehyde (MDA) content significantly at 21 and 28 days of heat stress, and promoted the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) from 14 through 28 days of heat stress. β-Sitosterol effectively improved heat tolerance through suppression of leaf senescence in creeping bentgrass exposed to heat stress in association with the alleviation of membrane lipid peroxidation and activation of the enzymatic antioxidant system.

Open Access

Heat-induced leaf senescence has been associated with stress-induced oxidative damage. The major objective of this study was to determine whether exogenous application of β-carotene may improve heat tolerance in creeping bentgrass (Agrostis stolonifera cv. Penncross) by suppressing leaf senescence and activating antioxidant metabolism. Plants were subjected to heat stress at 35/30 °C (day/night) or at the optimal temperature of 22/18 °C (day/night), and were treated with either β-carotene (1 mm) or water (untreated control) by foliar spraying every 7 days for 28 days in controlled-environment growth chambers. β-Carotene application suppressed heat-induced leaf senescence, as demonstrated by an increase in turf quality (TQ) and leaf chlorophyll content as well as a reduction in electrolyte leakage (EL). β-Carotene-treated plants had a significantly lower malondialdehyde (MDA) content and significantly greater activity of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) from 14 through 28 days of heat stress, and ascorbate peroxidase (APX) activity from 21 through 28 days of heat stress. These findings suggest that β-carotene may promote heat tolerance by enhancing antioxidant activity to suppress leaf senescence.

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Understanding antioxidant mechanisms for heat stress is important for improving heat tolerance in cool-season plant species. The objective of this study was to identify antioxidant enzymes associated with cultivar variations in heat tolerance in kentucky bluegrass (Poa pratensis) by comparing heat responses of activity and isoforms of antioxidant enzymes in two cultivars contrasting in heat tolerance. Plants of heat-tolerant ‘Eagleton’ and heat-sensitive ‘Brilliant’ were exposed to 20 °C (control) or 40 °C (heat stress) for 28 days in growth chambers. Chlorophyll (Chl) a content remained unchanged and Chl b content increased in ‘Eagleton’, while both of them decreased in ‘Brilliant’, and by 28 days, ‘Eagleton’ had significantly higher Chl a and b content than ‘Brilliant’. The activities of superoxide dismutase (SOD) were significantly higher in ‘Eagleton’ than in ‘Brilliant’ by 28 days of heat stress. An isozyme SOD2 was induced early during heat stress in ‘Eagleton’, while isozyme SOD3 degraded, to a lesser extent in ‘Eagleton’ than in ‘Brilliant’. Catalase (CAT) activity significantly increased in ‘Brilliant’ but remained constant in ‘Eagleton’, and ‘Brilliant’ had a significantly higher CAT activity and isozyme CAT1 than ‘Eagleton’ during heat stress. Significant increases in ascorbate peroxidase (APX) activities occurred under heat stress, to a greater extent in ‘Eagleton’, whereas isozymes did not exhibit difference between cultivars. Guaiacol-peroxidase (POD) activity declined during heat stress in both cultivars. The intensity of POD isozymes in ‘Brilliant’ remained constant, while ‘Eagleton’ showed a transient increases in POD1 at 7 days of heat stress. Our results indicated that antioxidant defense mechanisms for heat tolerance in kentucky bluegrass could be mainly associated with changes in activity and forms of isozymes of SOD for O2 scavenging and APX activity for H2O2 scavenging under heat stress.

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Elevated CO2 may contribute toward plant tolerance to prolonged drought stress. The objective of this study was to investigate changes in protein abundance associated with mitigation of drought stress by elevated CO2 in leaves of a cool-season grass species used as fine turfgrass. Plants of creeping bentgrass (Agrostis stolonifera cv. Penncross) were grown at either ambient CO2 concentration (400 µL·L−1) or elevated CO2 concentration (800 µL·L−1) for 35 days under well-irrigated and fertilized conditions and then subjected to drought stress for 21 days by withholding irrigation. Plants exposed to elevated CO2 concentration maintained higher leaf water content, membrane stability, and visual turf quality (TQ) under drought stress compared with plants grown under ambient CO2 conditions. The abundance of proteins involved in photosynthetic carbon fixation and assimilation, including chloroplastic glyceraldehyde phosphate dehydrogenase A (GAPDH-A) and ribulose 1,5-bisphosphate carboxylase (RuBisCO) decreased less and the abundance of proteins involved in respiratory metabolism (i.e., cytosolic GAPDH) increased less during drought due to elevated CO2. The results suggest that elevated CO2 lessened growth and physiological damages during drought by facilitating ribulose 1,5-bisphosphate regeneration and adenosine triphosphate (ATP) production in photosynthesis and downregulating factors contributing to respiratory metabolism.

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Heat stress-induced or stress-accelerated leaf senescence is related to the accumulation of ethylene and loss of chlorophyll in cool-season grass species. The objective of this study was to determine whether foliar-spraying the ethylene inhibitor, aminoethoxyvinylglycine (AVG), may suppress heat-induced leaf senescence through effects on chlorophyll synthesis and degrading enzymes in creeping bentgrass (Agrostis stolonifera). Plants were maintained in environmentally controlled growth chambers under non-stress (22/17 °C day/night) or heat stress (35/30 °C day/night) temperature conditions for 25 days, and turf quality, electrolyte leakage, and chlorophyll content were measured to assess the extent of leaf senescence. Activities of chlorophyll-synthesizing and chlorophyll-degrading enzymes were quantified to determine whether AVG may regulate chlorophyll metabolism. Plants were foliar-sprayed with 25 µm AVG before and during heat stress at 7-day intervals. From 21 through 25 days of heat stress, AVG-treated plants had significantly higher turf quality and chlorophyll content, whereas electrolyte leakage was significantly lower in comparison with untreated controls. The activity of a chlorophyll-synthesizing enzyme, porphobilinogen deaminase, was significantly increased in AVG-treated plants at 21 days of heat stress. The activity of chlorophyll-degrading enzymes was significantly lower in plants treated with AVG from 14 through 25 days of heat stress for peroxidase, from 21 through 25 days of heat stress for pheophytinase, and at 25 days of heat stress for chlorophyllase. AVG may have suppressed heat-induced leaf senescence by regulating chlorophyll metabolic activities in cool-season grass species.

Open Access

Drought is a major limiting factor for turfgrass growth. Understanding genetic variations in physiological responses of turfgrass to drought stress would facilitate breeding and management programs to improve drought resistance. This study was designed to evaluate responses of abscisic acid (ABA) accumulation, water relations, and gas exchange to drought stress in four Kentucky bluegrass (Poa pratensis L.) cultivars differing in drought resistance. Plants of `Midnight' and `A82-204' (drought resistant) and `Brilliant' and `RSP' (drought susceptible) were grown under well-watered (control) or drought stress conditions for 25 days in growth chambers. Turf quality, leaf water potential (Ψleaf), relative water content (RWC), leaf net photosynthesis rate (Pn), and stomatal conductance (gs) declined, while electrolyte leakage (EL) increased during drought progression in all cultivars. The magnitudes of the change in these parameters were greater for `RSP' and `Brilliant' than for `Midnight' and `A82-204'. Leaf ABA content in `RSP' and `Brilliant' increased sharply after 2 days of stress to as much as 34 times the control level at 10 days of drought. Leaf ABA content in `Midnight' and `A82-204' also increased with drought, but to a lesser extent than in the other two cultivars. Leaf ABA level was negatively correlated with Ψleaf and gs. `A82-204' had a significantly lower ABA accumulation rate with changes in Ψleaf during drought compared to `Midnight', `RSP' and `Brilliant'; however, no differences in ABA accumulation rate were detected among the latter three cultivars. In addition, leaf gs was more sensitive to changes in ABA accumulation in `Midnight' and `A82-204' than in `RSP' and `Brilliant'. These results demonstrated that drought tolerant cultivars of Kentucky bluegrass were characterized by lower ABA accumulation and less severe decline in Ψleaf, Pn, gs, and turf quality during drought stress than drought sensitive cultivars. Drought tolerance of Kentucky bluegrass could be related to sensitivity of stomata to endogenous accumulation of ABA under drought stress conditions.

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Osmotic adjustment (OA) is a major physiological mechanism associated with maintenance of cell turgor in response to dehydration stress. The objectives of this study were to examine changes in capacity for OA in relation to plant tolerance to drought stress for two cool-season turfgrass species, creeping bentgrass (Agrostis stolonifera L.) and velvet bentgrass (A. canina L.), and to determine major solutes contributing to OA in these grass species. Plants of `L-93' creeping bentgrass and `Greenwich' velvet bentgrass were grown in a growth chamber in polyvinyl chloride (PVC) tubes (5 cm diameter, 40 cm high) filled with a 1:3 (v/v) sterilized mixture of sand and sandy loam soil. The experiment consisted of two soil moisture treatments: 1) well-watered control, irrigated three times per week to maintain soil moisture near pot capacity; and 2) drought stress, irrigation completely withheld. Velvet bentgrass exhibited higher drought tolerance compared to creeping bentgrass, as manifested by higher visual turfgrass quality (TQ) and leaf relative water content (RWC) under drought stress. Both creeping bentgrass and velvet bentgrass exhibited OA in response to drought stress; however, velvet bentgrass exhibited 50% to 60% higher magnitude of OA, which could be related to the maintenance of higher leaf RWC and TQ for greater drought duration compared to creeping bentgrass. OA for both creeping bentgrass and velvet bentgrass was associated with accumulation of water soluble carbohydrates during the early period of drought and increases in proline content following prolonged period of drought; however, inorganic ion content (Ca2+ and K+) did not considerably change under drought stress and did not seem to contribute to OA in these species.

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Efficient carbon distribution and utilization may enhance drought survival and recovery ability for perennial grasses. The objectives of this study were to examine changes in carbon partitioning and carbohydrate accumulation patterns in shoots and roots of colonial bentgrass (Agrostis capillaris L.), creeping bentgrass (A. stolonifera L.), and velvet bentgrass (A. canina L.) in response to drought and re-watering following drought, and to determine whether species variation in drought tolerance and recuperative potential is related to differences in the patterns of carbon partitioning and accumulation. The experiment consisted of three treatments: 1) well-watered control; 2) drought, irrigation completely withheld for 18 days; and 3) drought recovery, a group of drought-stressed plants were re-watered at the end of the drought treatment (18 days). Drought tolerance and recuperative ability of three species was evaluated by measuring turf quality and leaf relative water content. These parameters indicated that velvet bentgrass was most drought tolerant while colonial bentgrass had highest recuperative ability among the three species. Plants were labeled with 14CO2 to determine carbon partitioning to shoots and roots. Carbohydrate accumulation was assessed by total nonstructural carbohydrate (TNC) content. The proportion of newly photosynthesized 14C partitioned to roots increased at 12 days of drought compared to the pre-stress level, to a greater extent for velvet bentgrass (45%) than for colonial bentgrass (35%) and creeping bentgrass (30%). In general, the proportion of 14C was highest in roots, intermediate in stems, and lowest in leaves at 12 days of drought treatment for all three bentgrass species. As drought duration and severity increased (18 days), 14C partitioning increased more in leaves and stems relative to that in roots for all three species. Stem TNC content was significantly greater for drought-stressed plants of colonial bentgrass and velvet bentgrass compared to their respective well-watered control plants, whereas no differences in stem TNC content were observed between drought-stressed and well-watered creeping bentgrass. Our results suggest that increased carbon partitioning to roots during initial drought stress represented an adaptive response of bentgrass species to short-term drought stress, and increased carbon partitioning and carbohydrate accumulation in stems during prolonged period of drought stress could be beneficial for rapid recovery of turf growth and water status upon re-watering.

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Previous investigations identified velvet bentgrass (Agrostis canina L.) as having higher drought resistance among bentgrass species. This study was designed to determine whether species variation in drought resistance for colonial bentgrass (A. capillaris L.), creeping bentgrass (A. stolonifera L.), and velvet bentgrass was associated with differences in antioxidant enzyme levels in response to drought. Plants of ‘Tiger II’ colonial bentgrass, ‘L-93’ creeping bentgrass, and ‘Greenwich’ velvet bentgrass were maintained in a growth chamber under two watering treatments: 1) well-watered control and 2) irrigation completely withheld for 28 d (drought stress). Prolonged drought stress caused oxidative damage in all three bentgrass species as exhibited by a general decline in antioxidant enzyme activities and an increase in lipid peroxidation. Compared among the three species, velvet bentgrass maintained antioxidant enzyme activities for a greater duration of drought treatment compared with both colonial bentgrass and creeping bentgrass. Higher antioxidant enzyme capacity for velvet bentgrass was associated with less lipid peroxidation and higher turf quality, leaf relative water content, and photochemical efficiency for a greater duration of stress compared with colonial bentgrass and creeping bentgrass. These results suggest that bentgrass resistance to drought stress could be associated with higher oxidative scavenging ability, especially for velvet bentgrass.

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